This invention relates generally to fabricating temporary and semi-permanent bridges and to temporization where multiple teeth are involved. More particularly, this invention extends the concepts for constructing and using shells for temporary and provisional crowns, as disclosed in Applicant""s prior patent applications (including U.S. Pat. No. 6,068,481, U.S. Ser. No. 09/178,023 filed Oct. 23, 1998, PCT/US98/22813, and Ser. No. 60/131,817, filed Apr. 29, 1999, each herein incorporated by reference), to the creation of temporary and semi-permanent bridges and multi-tooth crowns.
Applicant""s prior applications disclose flexible dimension crown shells and methods of making temporary and long-term provisional dental crowns using such shells. As noted in those applications, three primary methods have been used for fabricating temporary and provisional crowns. In a first technique, conventional prefabricated crown forms or shells, made of a metal such as aluminum or stainless steel, or of a polycarbonate such as the Ion crown forms sold by 3M Corporation, are trimmed and shaped to fit a prepared tooth. Examples of temporary crowns of this type are disclosed in U.S. Pat. No. 4,015,332 (Manne), U.S. Pat. No. 4,678,435 (Long), U.S. Pat. No. 4,778,386 (Spiry), and U.S. Pat. No. 5,458,489 (Tennyson).
A second technique calls for making an impression of the tooth before the tooth is prepared for a crown. After the impression is made, the tooth is prepared and the impression, filled with a bis-acryl material, is placed over the prepared tooth. After the bis-acryl material sets, it is removed from the dental impression, and then trimmed, polished, and seated in the mouth.
A third primary technique proceeds by placing a putty-like ball of polymethyl-methacrylate over a prepared tooth. The patient then bites down and the material begins to set. Before it completely sets, the putty-like material is removed from the tooth, trimmed and placed back on the tooth. Once the material sets, it is then trimmed again and the bite adjusted. Finally, the temporary crown is cemented to the tooth. In a variation of this technique, as disclosed in U.S. Pat. No. 5,385,469, a tubular dental form for forming a universal crown in situ is used.
Each of these techniques has various advantages and disadvantages. Using prefabricated forms, as in the first technique, for example, is fast and simple, but the fit of conventional pre-formed shells is not very good. The margins, in particular, do not fit well. Specifically, it is hard to get good proximal contact to adjacent teeth, and the contours and occlusion are not always good. Some manufacturers try to overcome these drawbacks by proliferating sizes and shapes of shells, with some selections providing as many as 80 different sizes and shapes of molars and bicuspids. Unfortunately, this attempted solution is expensive in terms of materials and also in terms of the time required for the dentist to pick the right shell.
Manne adds a degree of freedom to the first technique by providing an incisor shell that has slits in its mesio-distal sides to permit the shell to flex in the labio-lingual direction about a hinge axis located at the occlusal surface. Long also provides a degree of freedom in this technique by providing open mesio-distal sides to permit the acrylic resin filler material to protrude proximally to contact adjacent teeth. These shells, like others used in this technique, require trimming the free edges of their buccal and lingual sidewalls to ensure a good fit along the gingival margins, as well as a good occlusion. Trimming and fitting is time-consuming for the dentist and the patient.
The second technique gives good contours and bite accuracy, but making an impression is time-consuming. Furthermore, neither the strength nor the durability of temporary crowns produced by this technique are very good. Furthermore, the impression cannot be made if the patient""s tooth is already broken when initially treated. The third technique, namely, free-forming a temporary crown of putty-like material, can be accurate and fairly fast compared to the other techniques, but only if performed by a skilled dentist or technician.
Another main problem with the third approach is that it is very technique-sensitive. A dental technician must be highly skilled in order to accurately carve the tooth anatomy into the tooth replacement. A still further problem with this technique is that special care must be taken to ensure that the patient""s mouth is not injured by the exothermal reaction involved in curing the crown material.
All of the foregoing techniques are undesirably slow. Even the fastest of these techniques generally takes half an hour or more of work for the dentist to fit a temporary or provisional crown to a patient. Additionally, the crowns resulting from the second and third techniques are typically not very durable and are therefore not well-suited for long-term wear. Although the stainless steel shells of the first technique are very durable, it is more difficult to fit stainless steel shells to the patient and to grind the shells"" occlusal surfaces to get a comfortable bite.
Applicant""s prior inventions improve over each of these techniques by providing durable shells that are sized and shaped to simplify the crown forming process. In general, the technique disclosed in Applicant""s earlier applications combines the best aspects of two of the conventional techniques, namely, the free-form and specially-designed shell techniques. Specifically, shells according to applicant""s prior invention include an occlusal top wall, buccal and lingual sidewalls, and mesio-distal sidewalls. The occlusal surface of the top wall approximates the occlusal surface of a natural tooth. A window is provided in at least one of the mesio-distal sidewalls. A resin is used to fill the shell. The resin is shape-controlled by the shell and the windows provided therein. This shape control saves the dentist valuable time in shaping the temporary or long-term provisional crown.
The mesio-distal sidewalls of the shells can also each include a recessed area adjoining the windows that receives and retains protruding resin in proximal contact with adjacent teeth. Each recessed area preferably forms a concavity conforming to the convexity of the mesio-distal side of the respective adjacent tooth. The shells can also have short labial and lingual side walls so that no trimming of the shells themselves is needed. This, too, saves the dentist a great deal of time. The shells also give the dentist several degrees of freedom, so that most molars and bicuspids can be fitted using a limited range of sizes and shapes of shells. These shells, and the method of using them thereby offer substantial advantages over the prior art.
Despite the improvements offered by applicant""s prior inventions described above, neither it, nor any of the other prior art techniques, readily facilitate the preparation of multiple crowns at the same time. They also do not address the use of shells in preparing bridges to replace missing teeth.
Prosthodontics involves the replacement of missing teeth and related mouth or jaw structures by bridges, dentures, or other artificial devices. Bridges, in particular, are prosthodontic devices used to replace one or more missing teeth as well as to restore one or more damaged teeth. Bridges typically consist of a cast member that bridges the edentulous space (gap) caused by a missing tooth or teeth. The bridge is generally supported by adjacent natural teeth, called abutment teeth.
Unfortunately, most present methods for constructing bridges are unduly time-consuming and complex. Installing a permanent bridge is generally prefaced by the construction and installation of a temporary bridge. Temporary bridges are typically necessary because the process of constructing the permanent bridge is time consuming. The temporary bridge is used to provide temporary tooth replacement while the permanent bridge is being prepared.
Even preparing and installing temporary bridges, however, is generally more complex, time consuming, and expensive than desirable. Some prior art techniques involve the creation of custom molds and impressions that are patient-specific. These techniques are expensive and burdensome because they require a large amount of dentist time. Other techniques involve prefabricated dental pontic assemblies and connectors or molds. While these techniques offer some improvement over custom-formed assemblies, they too have shortcomings.
One approach to constructing a temporary bridge using a prefabricated mold is disclosed in U.S. Pat. No. 5,803,737 (xe2x80x9cLyalinxe2x80x9d). More particularly, Lyalin discloses providing multiple preformed molds for use in preparing a temporary bridge. Each preformed mold is horse-shoe shaped and comprises sixteen recesses. Each recess is formed internally to mold the external shape of a corresponding tooth. The pre-formed molds can be made in various arch shapes and tooth lengths and widths to permit selection of a mold that more closely matches a patient""s dentition. Once the appropriate preformed mold is selected, a desired subsection of the mold is sectioned off from the rest of the mold and used to form the bridge.
To form the bridge, the selected mold subsection is filled with an acrylic resin and emplaced over the edentulous space and prepared abutment teeth while the resin is allowed to cure. Once set, the mold subsection and hardened resin are removed from the mouth. The cast bridge is then removed from the mold, trimmed as necessary, and then secured in the patient""s dentition over the endentulous space and on top of the abutment teeth to form a temporary bridge.
Despite the improvements offered by prior art prosthodontic devices such as the Lyalin device, a need remains for a method of making temporary and semi-permanent bridges and multi-tooth crowns that is quick and accurate, that provides a good fit without substantial trimming, that is durable enough for long-term use, and that is inexpensive. Likewise, an improved bridge and multi-tooth crown shell is also desirable.
It is, therefore, an object of the present invention to simplify the fabrication, fitting, and installation of temporary and semi-permanent bridges and multi-tooth crowns.
Another object of the present invention is to make temporary and semi-permanent bridges and multi-tooth crowns that fit well and are durable enough for long-term use.
A further object is to make bridges and multi-tooth crowns that fit well but are inexpensive both in terms of materials and time taken to fit them.
The term xe2x80x9cquadrant dentistryxe2x80x9d is used to refer to the dental practice of restoring multiple teeth in one quadrant (i.e., lower left, lower right, upper left, or upper right) of the mouth. In general, the present invention builds on applicant""s prior inventions by providing a multi-tooth shell and technique for performing quadrant dentistry. The invention is also applicable to replacing or restoring anterior teeth.
A multi-tooth shell according to the present invention is obtained by forming an integral quadrant or anterior shell including multiple single-tooth shell segments. A multi-tooth shell could also be made to include teeth from both a quadrant and an anterior region. The multi-tooth shells are formed as a series of single-tooth shell segments, wherein each segment has the external shape of a corresponding tooth and a central cavity shaped to fit loosely over a prepared tooth. A quadrant shell, for instance, can include segments corresponding to cuspids, bicuspids, and molars, that are integrally molded as a shell unit. The quadrant shell can also be fitted into a patient""s mouth as an integral unit. Although the quadrant shell can be made to encompass any number of multiple teeth, e.g. two or three or more, it is preferably made to encompass four, or most preferably, five teeth.
The four-tooth quadrant shell embodiment preferably provides either two molars and two bicuspids, or one molar, two bicuspids, and a cuspid, in the order normally occurring in human dentition. The five-tooth embodiment preferably comprises one cuspid, two bicuspids, and two molars. In yet another alternative embodiment, the quadrant shell could be made to correspond to just three teethxe2x80x94such as a cuspid and two bicuspids, two bicuspids and a molar, or a biscuspid and two molars.
A method for using a shell of the present invention to form a temporary or semi-permanent bridge is also provided. A typical bridge includes three teeth. Therefore, in preparing a typical bridge using a four-tooth quadrant or anterior shell, a shell segment at one end of the shell is cut off by the dentist to leave a three-segment shell section that covers the missing tooth and the abutment teeth. In a five-tooth embodiment, either two adjacent shell segments at one end of the shell or individual shell segments at each end of the shell, as appropriate, are cut off to leave the desired three-segment shell section.
Regardless of the number of segments in the original shell, however, the selected three-segment shell section consists of integrally-connected shell segments for three consecutive teeth. Once the three-segment section is obtained, it is filled with acrylic resin and mounted in the patient""s dentition. Specifically, the end shell segments are emplaced on prepared abutment teeth on opposite sides of a gap in the patient""s dentition, with the middle shell of the bridge unit, used to form the pontic, spanning the gap. As the endmost shells are fitted onto the patient""s prepared teeth, a portion of the resin extrudes along the gingival margins and from windows at the ends of the shell section to form a good proximal contact with adjacent teeth. The windows can either be partial openings formed in mesio-distal sidewalls of the quadrant shell, or they can be open mesio-distal sides.
With only minor modifications to the above technique, the shells of this invention can also be used to provide a bridge where more than one tooth is missing. If, for example, two adjacent teeth are missing, either the four- or five-segment embodiment of the invention can be used to prepare a bridge. If the four tooth embodiment is used, no cutting of the shell is necessary and the entire shell provides the section used to form the bridge. In the five-segment embodiment, one segment at the appropriate end is removed to leave a four-segment section for forming the bridge. Shells having more than five segments are also contemplated by this invention and could be used in a similar way.
These same shells can also be used by a dentist to provide multi-tooth crowns for adjacent prepared teeth. To provide a multi-tooth temporary or provisional crown, an appropriate multi-tooth shell is selected and sectioned, if necessary, to leave a fused hollow shell section having multiple interconnected shell segments corresponding to just the prepared teeth. This shell section is then filled with resin, placed on the prepared teeth, and left there until the resin has set. Once the resin has set, the resulting unfinished crown is removed from the prepared teeth and adjusted as necessary to fit comfortably within the patient""s dentition. The finished multi-tooth crown forms a composite structure is then cemented onto the prepared teeth. As an added benefit of this invention, the remaining, unused shell segments can be saved and used at another time for preparing crowns for teeth corresponding to those unused segments.